As most of you probably know, Steven Spielberg and Peter Jackson‘s The Adventures of Tintin, which will be released next week, was originally called The Adventures of Tintin: The Secret of the Unicorn. Though the subtitle was dropped and the film pulls from several stories, that’s the primary Herge book this first film is based on. The legendary author published about two dozen Tintin books in total but, instead of starting with the first one, Spielberg and Jackson opted to jump into the middle (Unicorn was the 11th book) because it introduced a very popular sidekick character in Captain Haddock.

Since they didn’t lock themselves into a specific time in the Tintin mythology, there’s been much discussion about which story the potential sequel, directed by Jackson and produced by Spielberg, would follow. The main rumor was Prisoners of the Sun, but that was reportedly pushed to a possible third movie. Not the case says producer Kathleen Kennedy.

In a new interview, she says while a screenplay for a sequel is currently being written by Anthony Horowitz, Prisoners of the Sun won’t be the basis of the second or third film. The sequel may, however, center on The Calculus Affair. Read more below.

The Playlist caught up with Kennedy, Spielberg’s former assistant turned mega-producer, to discuss Tintin and its sequels. Here’s what she said about Prisoners of the Sun:

‘Prisoners of the Sun’ was a very, very early discussion, and it isn’t under discussion anymore. We’ve still got Anthony Horowitz working on the second movie, and we don’t know what we’re doing with the third movie yet.

But what about the second movie? Kennedy said they pulled from several stories for The Adventures of Tintin because they knew they had to introduce specific characters and the sequel would be similar:

So now what we’re thinking [for the second film] is what new characters do we want to introduce? Well, we’ll probably introduce Calculus and bring him into the fold.

So does that mean the second movie will, definitely, be The Calculus Affair, as it’s Professor Calculus’ most famous story?

We haven’t decided yet but that’s the direction we’re headed.

Kennedy recently stated the sequel could, possibly, be out by Christmas 2014, just one year after director Peter Jackson’s second Hobbit film is released. And while that’s by no means set in stone, she explained how that would even be possible with Spielberg directing numerous films and Jackson finishing The Hobbit:

It’s tricky getting everybody but that’s how we did the first movie, sort of passing the baton. When Steven was available, he’d jump in, and when he was busy, Peter would pick up the slack. It was kind of amazing how they’d work together. We never knew how this would work, but it worked out really, really well.

Do you think Professor Calculus is an integral part to a Tintin sequel? Can the movie be done in a mere three years?